This research project is concerned with assessing the significance of environmental influences on blood pressure regulation and the etiology of hypertension. The experimental strategy involves determining the hemodynamic basis of blood pressure changes associated with environmental stressors and the neural-humoraa mechanisms by which these are controlled. Also, being determined are the qualities of environmental stressors which appear most significant in modifying blood pressure. Both a chronic dog preparation and young adult humans with a labile blood pressure are used as subjects. Several hypotheses andquestions are being investigated. Among these are: (1) The respective role of cardiac output and peripheral resistance in modifying blood pressure. Available evidence points to beta-adrenergic influences on myocardial force and heart rate as being of prime importance. (2) The influence of environmental stressors on kidney blood flow and the renin-angiotensin mmchanism. (3) The significance of stimulus parameters such as stress intensity and the necessity for the organism to actively cope. Available evidence indicates that beta-adrenergic influence are most appreciable when the organism actively copes with the stressor in contrast to passively accepting them as in learned helplessnes. (4) The relationship of beta adrenergic influences to O2 consumption. This aims to determine the extent tissues may be over-perfused when beta-adrenergic influences on cardiac output are maximal and whether over-perfusion initiates autoregulatory mechanisms which act to perpetuate hypertensive effects. (5) The respective role of vagal and sympathetic influences on the heart and the central nervous system mechanisms which modulate each influence.